An unmanned submarine at the Naval Surface Warfare Center’s Carderock Division, in Bayview, Idaho. (Jeff T. Green — Getty Images)

And when it comes to military secrets, there’s one field in which foreign adversaries have shown a particular interest lately: underwater drones.

The Navy has made unmanned systems a priority in recent years, and the recently retired chief of naval operations made them a bedrock of his vision for the future of the fleet.

That emphasis has apparently not gone unnoticed.

In a recent report, the Defense Security Service, a Pentagon agency that oversees information technology security, concluded that private contractors increasingly documented “suspicious contacts” over the past year suggesting that adversaries were seeking data on underwater drones.

Foreign governments, the report said, have not yet “achieved the U.S. level of overall industrial development nor the capability for military applications.”

“Access to more advanced AUV [autonomous underwater vehicles] technology would allow the regions to both accelerate the implementation of improved underwater systems and save time and money by obtaining and reverse-engineering.”

The report analyzed reports of attempts to gain unauthorized access to a wide variety of government and industry secrets. But the authors said they singled out underwater drones as a “growing collection area.”

Overall, among private contractors, the number of suspicious contact reports to DSS more than doubled from fiscal 2009 to fiscal 2010.

The report released Thursday by the Office of the National Counterintelligence Executive singled out China and Russia as presenting the most significant cyber-espionage threat. The Defense Security Service did not identify trends in individual countries, but it didn’t leave much room for mystery, either.

The vast majority of suspicious attempts to gather information on underwater drones originated in “East Asia and the Pacific,” it said.